Newborn mammals must acquire milk to survive. The stretch response, an example of species-typical motor behavior that typically occurs during suckling at the nipple, recently has been identified in the rat fetus. Using techniques that permit direct observation of healthy rodent fetuses and controlled presentation of chemosensory fluids to fetal subjects, it is now possible to apply experimental methods to study the stretch response and other aspects of behavior of the developing mammalian fetus in its environment. Because the fetus lacks specific experience with milk and does not require milk for its sustenance, responsiveness to milk can be studied in naive subjects over a range of prenatal ages. Moreover, study of the fetus obviates some of the complexities of studying the newborn, which by necessity must be removed from its homeostatic relationship with the mother to permit measurement of motor and sensory abilities. The prenatal period thus provides a unique testing ground for investigating the control and development of behavioral patterns that become functionally important after birth. Study of the fetal stretch response will serve as an animal model of prenatal motor development with direct relevance for postnatal behavior. In this proposal, we will: (a) investigate sensory factors that influence the expression of the stretch response, (b) characterize changes in motor behavior that organize the stretch response, (c) manipulate fetal behavior to promote earlier developmental expression of the stretch response, and (d) examine the interaction of fetal responses to milk and other sensory-based behavior. The concept of self-organization will be applied to the study of fetal behavioral responses to milk as a model for understanding the process of developmental change.